Hydrogen storage container and mixture therein

ABSTRACT

This invention relates to a new kind of hydrogen storage mixture and container thereof. This hydrogen storage container consists of a container casing, a hydrogen storage mixture and a valve. The hydrogen storage mixture loaded inside the container is made of hydrogen storage alloy granules and metal fibers and/or non-hydrogen-absorbing alloy fibers that do not absorb hydrogen. The non-hydrogen-absorbing fibers are dispersed among the hydrogen storage alloy granules and form a network structure. The non-hydrogen-absorbing fibers include non-hydrogen-absorbing metal fibers and/or non-hydrogen-absorbing alloy fibers, or their mixture. In the hydrogen storage mixture, the weight ratio of the non-hydrogen-absorbing fibers to the hydrogen storage alloys is about  0.01˜0.1 . The hydrogen storage installation adopting the technology of this invention can effectively prevent the metal hydride granules from moving over a comparatively long distance and accumulating in some locations in the container during hydriding and dehydriding, and also can improve the thermal conductivity of the hydrogen storage mixture inside the container. The hydrogen storage container of this invention is easy to manufacture, safe to use, and low in cost. This invention can be used for the manufacture of hydrogen storage containers for hydrogen storage, transport, compression and purification.

FIELD OF THE INVENTION

The present invention relates to hydrogen storage, transport and compression technology, more specifically, to a hydrogen storage equipment and a related hydrogen storage mixture.

DESCRIPTION OF THE RELATED ART

Hydrogen is an important industrial raw material. It is also an ideal clean fuel and a secondary energy source for the future. Presently, there are three main methods for storing and transporting hydrogen, namely high-pressure containers (steel or aluminum alloy tanks), liquid hydrogen containers (low temperature Dewar flasks) and metal hydride hydrogen storage containers. The most distinct advantages for using metal hydride hydrogen storage containers to store and transport hydrogen are its higher level of storage and transport safety, and the higher volume hydrogen storage density (the mass of hydrogen stored in a definite container volume) than storage in a high pressure container or in a liquid hydrogen storage container of the same volume. Special attention has been paid to the development of the metal hydride hydrogen storage technique because of the various functions it is able to serve, including the purification, separation and recovery of hydrogen, hydrogen compression and the ability to serve as a medium for energy exchange systems, such as heat storage, space heating, air conditioning and refrigeration systems. The market prospect of this technology has recently become very positive as the technology of using high purity hydrogen as the fuel in fuel cells is becoming mature and is more widely used in automobiles, motor cycles, scooters, power sources for computers, video cameras, power tools, military equipments and standby electric stations. For all these applications, reliable and efficient hydrogen storage containers are indispensable.

A hydride hydrogen storage container is readily formed by loading a proper amount of hydrogen storage alloy granules into a pressure tank with a suitable gas regulating valve. During hydrogen absorbing and desorbing, there is a heat effect, whose value varies depending on the adopted hydrogen storage alloy. Generally, the heat effect value is in the range of 25˜75 KJ/mole. Due to this heat effect, to expedite the hydrogen absorbing and desorbing processes, a definite amount of heat must be smoothly transferred into or out of the container. Otherwise, the temperature of the storage tank will change rapidly. During hydrogen absorption, the alloy undergoes a volume expansion at a rate in the range of 14˜25%. Because of the volume expansion, the alloy breaks into smaller granules and finally to fine powders. This process is called decrepitation, which keeps on going as the hydriding/dehydriding cycle repeats. The rate of the decrepitation (particulation) increases rapidly in the beginning, then slows down gradually and stabilizes at the end.

However, there are several problems with the hydrogen-absorbing method. On one hand, as the heat conductivity of hydrogen storage alloys is intrinsically rather poor, being equivalent to that of broken glass or sand, it is rather difficult to make heat transfer into/out of a hydride bed. Because of the poor heat transfer, the temperature of a hydride hydrogen container usually increases rapidly during the hydrogen absorbing process and drops rapidly during the hydrogen desorbing process. The change of the container temperature greatly slows down the rate of hydriding or dehydriding or even stops the process completely. On the other hand, the fine particles of hydrogen storage alloy and its hydride are very flowable, and are easily propelled around by the incoming and outgoing hydrogen stream during the hydriding and dehydriding processes. The particles settle down and compact into rather solid masses in certain localities of the container, where the volume expansion of the alloy during hydriding generally causes local deformation or even breakage of the container. Therefore, the key technical problems to be solved include the increase of the thermal conductivity of the hydride bed and the prevention of the free movement of hydrogen storage granules inside the container during the hydrogen charging/discharging processes. The following endeavors have been made to solve these problems.

The reference of M. Ron and M. Elemelach, Heat transfer characteristics of porous metallic matrix metal-hydrides, Proceeding of International Symposium on Hydrides for Energy Storage, Pergamon, Oxford, 1978, pp. 417-430 and M. Ron, D. Gruen, M. Mendelsohn and I. Sheft, Preparation and properties of porous metal hydride compacts, Journal of the Less-Common Metals, Vol. 74, 1980, pp. 445-448 explained the authors' endeavor to form metallic pellets by mixing and sintering the hydrogen storage alloy powder with the powder of a metal powder, such as aluminum, copper or nickel powder that does not absorb hydrogen (non-hydrogen-absorbing). The trial was a failure because no adequate room was provided in the pellets for the expansion of the hydrogen storage alloy granules, which decrepitate during hydriding. A modified process was proven technically acceptable, in which the hydrogen storage alloy granules were firstly made to absorb and desorb hydrogen for many cycles, and then were doped with SO₂ in the hydrided state, to keep the fine powder under the volume expansion state. The next step was mixing the doped powder with the powder of a non-hydrogen-absorbing metal to compress and sinter the mixture into pellets. The pellet formed in this way could stand more than 1000 hydriding/dehydriding cycles without any evident breakage. However, the process, as stated above, is complicated. In addition, the doping and sintering treatments may lower hydrogen storage capacity by about 15%.

According the reference of Qi-dong Wang, Jing Wu and Hui Gao, Vacuum sintered porous metal Hydride Compacts, Z. füer Phys. Chem., Vol. 164, 1989, pp. 1367-1372, the authors introduced an improved technique, in which the hydrogen storage alloy granules were firstly mixed with a definite amount of aluminum powder and a cavity-forming material (certain low temperature salt), then the mixture was pressed into pellets under pressure, and the pellets were baked at 60˜80° C. to remove the cavity-forming low temperature salt. Finally, the pellets were sintered under vacuum conditions. Pellets made in this way could undergo 1000 hydriding and dehydriding cycles without breakage because the cavities provide adequate room for volume expansion. Although the hydriding/dehydriding process and the doping process in the previous technique were omitted, thus its cost was reduced, the problem of lowered hydrogen storage capacity by about 15% still persisted.

The reference of H. Ishikawa, K. Oguro, A. Kato, H. Suzuki and E. Ishii, Preparation and properties of hydrogen storage alloy-copper microcapsules, Journal of the Less-Common Metals, Vol. 107, 1985, pp. 105-110 introduced a copper electroplating and compressing process, in which the cohesive force of plated copper film to form pellets with proper cavities is used. In this technique, hydrogen storage alloy granules were firstly subjected to a hydriding and dehydriding cycling treatment for more than 10 cycles and then sensitized and plated electrodelessly with copper in a solution. The copper plated alloy granules were then compressed under high hydrostatic pressure into blocks of different forms such as rings and hollow tubes to fit into specific hydrogen storage containers. The blocks prepared by this method can withstand about 1000 hydriding/dehydriding cycles without any breakage. The drawbacks for this process were also the high cost due to the initial hydriding/dehydriding, copper-plating and hydrostatic compression and vacuum sintering processes. The hydrogen storage capacity was reduced by about 10% because the plated copper layer does not absorbe hydrogen.

According to the reference of J. J. Reilly and J. R. Johnson, The kinetics of the absorption of hydrogen by LaNi₅H_(x)-n-undecane suspensions, Journal of the Less-Common Metals, Vol. 104, 1985, pp. 175-190 and J. J. Reilly, J. R. Johnson and T. Gamo, The effect of methane on the rate of hydrogen absorption by LaNi₅H_(x) in liquid suspension, Journal of the Less-Common Metals, Vol. 131, 1987, pp. 41-49, the National Brookhaven Laboratory of the United States initiated another new approach. The hydrogen storage alloy slurry, in which an organic liquid such as octane, ortho-decane or silicon oil was added into a container to form a slurry of the organic liquid and the hydrogen storage alloy powder. The powder was suspended in the liquid when agitated. Hydrogen could permeate through the organic liquid, and the hydrogen storage alloy granules hydride/dehydride reversibly as usual. In this process, the heat transfer property of the unit was improved due to the free movement of granules in the liquid. The problem of decrepitation and the damage of containers were also solved for the same reason. However, due to the introduction of a large quantity of non-hydrogen-absorbing liquid, both the unit weight of the hydrogen storage container and the hydrogen volume density of hydrogen storage container are greatly reduced.

Another approach to solve these problems was introduced by a German corporation, HWT, Gesellschaft für Hydrid und Wasserstofftechnik (Catalog HWT 8601E and of HWT Gesellschaft für Hydrid und Wasserstafftechnik MBH, Postfach Germany). According to this technique, each hydrogen container contains a certain number of standardized stainless steel tubes for holding the hydrogen storage alloy granules. The space inside each of the stainless steel tubes is separated into many small compartments by utilizing a corresponding number of punched stainless steel disks. The external diameters of the disks are carefully machined to fit into the inner cavity of the stainless tubes, so that the movement of the hydrogen storage granules is limited in small cavities confined by the tube cavity and two neighboring disks. Hydrogen is filled into each cavity by placing in the center of each tube a thin sintered stainless steel rod. The rod is not only porous enough for hydrogen to flow inside it and into or out of each subdivided cavity in the large tube around it, but the pores are small enough to prevent the escape of alloy granules. The space between the container and tubes is filled with water, which serves as the cooling or heating medium for keeping the temperature of the tubes constant during hydriding and dehydriding. As the movement of hydride granules is limited in small cavities, the problem of high compaction in certain region and the excessive expansion forces is also solved. The service life of the container of this design was reported to be very long. However, the initial cost of the containers of this design was the highest due to the costs of materials, precision machining and assembly.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a new kind of hydrogen storage container and the related hydrogen storage mixture. In this invention, a mixture of hydrogen storage alloy granules and non-hydrogen-absorbing metal and/or alloy fibers are placed into the container so that the metallic fiber forms a network to constrain the movement of the hydride granules in a very limited space in order to avoid heavy compaction of alloy granules into some locality of the container, which causes the deformation and rupture of the container on hydriding. The higher heat conductivity of the metallic fiber matrix also improves the heat transfer in the hydrogen container to facilitate the hydriding and dehydriding process.

This kind of hydrogen storage container provided by the present invention consists of a container casing, a hydrogen storage mixture and a valve. The hydrogen storage container according to the present invention has the following features. A mixture for reversibly storage of hydrogen is loaded inside the container, the mixture is made of hydrogen storage alloy granules and fibers of non-hydrogen-absorbing metals and/or their alloys. The non-hydrogen-absorbing fibers disperse among the hydrogen storage alloy granules and form a network structure. The non-hydrogen-absorbing fibers include non-hydrogen-absorbing metal fibers and/or non-hydrogen-absorbing alloy fibers, or their mixture.

The non-hydrogen-absorbing metal fibers may be made of aluminum, or copper, or nickel, or a mixture of the fibers of the above mentioned metals.

The non-hydrogen-absorbing alloy fibers may also be made of aluminum alloy, or copper alloy, or nickel alloy, or a mixture of the fibers of the above mentioned alloys.

Alternatively, the non-hydrogen-absorbing metal and/or alloy fibers can be a mixture of the fibers of aluminum/aluminum alloy, copper/copper alloy, nickel/nickel alloy.

The non-hydrogen-absorbing metallic fibers may be cut into short sections in filar shape.

The non-hydrogen-absorbing metallic fibers may also be cut into short sections in strip shape.

The dimension of the aforesaid non-hydrogen-absorbing metal and/or alloy fibers are about 3˜20 mm in length and not more than about 2 square millimeter in cross section.

The hydrogen storage mixture inside the hydrogen storage container of the present invention is used for reversibly absorbing and desorbing hydrogen. The weight ratio of the non-hydrogen-absorbing fibers to the hydrogen storage alloys is about 0.01˜0.1.

For the hydrogen storage alloy used in the aforesaid mixture, either rare-earth based alloy, titanium based alloy, zirconium based alloy, or magnesium, calcium and alkaline-earth based alloy, or their hydride granules can be used.

The present invention has the following advantages:

1) It is a mixture of hydrogen storage alloy granules and non-hydrogen-absorbing metal and/or alloy fibers that is loaded into a hydrogen storage container. The fibers in the mixture have sufficiently large surface area and form a three dimensional network structure, which is able to prevent the free and relatively long distance movement and local accumulation of hydrogen storage granules in certain regions of the container.

2) Because the aforesaid non-hydrogen-absorbing metal and/or alloy fibers have a good thermal conductivity, the addition of the non-hydrogen-absorbing fibers into the hydrogen storage container effectively increases the thermal conductivity of the solid bed inside the container. Because the content of the fibers in the mixture is below 10%, sometimes only 1%, its effect on the reduction of the hydrogen storage capacity of the mixture is small.

3) The hydrogen storage alloy granules in this hydrogen storage container do not need any previous treatment, such as copper plating, compaction, doping, sintering or repeated hydriding/dehydriding cycling. There is no need to add any organic solvent into the containers. Due to the above reasons, the hydrogen storage containers of the present invention are of low cost, highly efficient, and are able to be operated safely for a long period of time.

4) This hydrogen storage container is easy to manufacture and has high operation efficiency. This kind of hydrogen storage containers can be used for both stationary hydrogen storage and mobile or even portable hydrogen storage including the fuel tanks for hydrogen fuel cells or for internal combustion vehicles.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an elevated sectional view of the hydrogen storage container and the hydrogen storage mixture therein of the present invention.

FIG. 2 shows the prospective view of the non-hydrogen-absorbing metal fibers.

FIG. 3 shows a detailed diagram of the non-hydrogen-absorbing alloy fibers in the mixture inside the hydrogen storage container of the present invention.

FIG. 4 shows a detailed diagram of the non-hydrogen-absorbing metallic fibers that are cut into short sections of filar shape.

FIG. 5 shows a detailed diagram of the non-hydrogen-absorbing metallic fibers that are cut into short sections of strip shape.

The definitions of the reference numerals are as follows: 1. container casing; 2. hydrogen storage alloys; 3. non-hydrogen-absorbing fibers; 4. valve; 5. non-hydrogen-absorbing metal fibers; 6. hydrogen storage alloy granules; 7. non-hydrogen-absorbing alloy fibers; 8. non-hydrogen-absorbing metallic fibers that are cut into short sections in filar shape; 9. non-hydrogen-absorbing metallic fibers that are cut into short sections in strip shape.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 illustrates a sectional view of the hydrogen storage container and the hydrogen storage mixture therein of the present invention. It is composed of a container casing 1, a hydrogen storage mixture and a valve 4. The hydrogen storage mixture loaded into the container is made of hydrogen storage alloy granules 2 and the fibers of non-hydrogen-absorbing metals and/or their alloys 3. The non-hydrogen-absorbing fibers disperse among the hydrogen storage alloy granules and form a network structure. The non-hydrogen absorbing fibers include non-hydrogen-absorbing metal fibers and/or non-hydrogen-absorbing alloy fibers, or their mixture. The container casing 1 also has a good thermal conductivity. The letter “A” represents the place where a sintered stainless steel filter plug is installed.

In the hydrogen storage mixture loaded into the hydrogen storage container of the present invention as shown in FIG. 2, the weight ratio of the non-hydrogen-absorbing fibers to the hydrogen storage alloys is about 0.01˜0.1.

In the hydrogen storage mixture loaded into the hydrogen storage container of the present invention as shown in FIG. 2, the non-hydrogen-absorbing metal fibers 5 are made of aluminum, or copper, or nickel, or a mixture of the fibers of the above mentioned metals. Similarly, the non-hydrogen-absorbing alloy fibers 7 (FIG. 3) are made of aluminum alloy, or copper alloy, or nickel alloy, or a mixture of the fibers of the above mentioned alloys. The non-hydrogen-absorbing metal and/or alloy fibers may also be a mixture of the fibers of aluminum and aluminum alloy, copper and copper alloy, nickel and nickel alloy.

FIG. 2 illustrates the prospective view of the non-hydrogen-absorbing metal fibers used in the hydrogen storage container, wherein the non-hydrogen-absorbing metal fibers 5 are aluminum fibers, or copper fibers, or nickel fibers. Reference numeral 6 denotes hydrogen storage alloy granules.

As shown in FIG. 3, the non-hydrogen-absorbing alloy fibers 7, which can be the fibers of aluminum alloy, or copper alloy, or nickel alloy are mixed with the hydrogen storage alloy granules 6.

As shown in FIG. 4 and FIG. 5, the non-hydrogen-absorbing metal fibers and/or non-hydrogen-absorbing alloy fibers can be cut into short sections of filar shape 8 or strip shape 9, each section being 3˜20 mm in length, and not more than 2 square millimeter in cross section.

The short sections of non-hydrogen-absorbing fibers have three-dimensional structures with rough surfaces. In an example of aluminum fibers, the specific weight of the mixture of the fibers and hydrogen storage alloy granules is less than that of hydrogen storage alloy granules alone. This indicates that there is more free space for the expansion of the alloy granules when absorbing hydrogen. More importantly, the fibers form a continuous three-dimensional space structure (or skeleton), which prevents the long distance movement of the granules and the accumulation of the granules in certain localities in the container.

The hydrogen storage alloy used inside the hydrogen storage container of the present invention, can be a rare-earth based alloy, titanium based alloy, zirconium based alloy, or magnesium, calcium and alkaline-earth based alloy, or their hydride granules.

Preferably, the non-hydrogen-absorbing fibers are chosen from some non-hydrogen-absorbing metal or alloy fibers with high thermal conductivity. For example, the thermal conductivity of Al, Cu and Ni is 222, 394 and 92 J/m·s·K, respectively, while the thermal conductivity of the hydride powder of TiFe and LaNi₅ is 1.49 and 1.32 J/m·s·K, respectively. The thermal conductivity of the metallic fiber is 60˜300 times higher than that of the hydride powder. As the fibers with high thermal conductivity are dispersed between the granules of hydrogen storage alloy or its hydride and form a three-dimensional space structure, the thermal conductivity of the mixture inside the hydrogen storage container is greatly improved.

EXAMPLE 1

A hydrogen storage container consists of a container casing, a hydrogen storage mixture and a valve. The hydrogen storage mixture loaded into the container is made of hydrogen storage alloy granules and non-hydrogen-absorbing aluminum fibers. Hydrogen storage alloy MmNi_(4.5)Mn_(0.5) used in this example belongs to the rare-earth based hydrogen storage alloys; Mm stands for the cerium-rich mischmetal. The ingots of MmNi_(4.5)Mn_(0.5) should be crushed into small granules with a diameter of about 3 mm before being loaded into the container. The average length of the aluminum fibers is about 3 mm and average cross section is about 0.5 square millimeters. The total weight of aluminum fibers is about one percent of the total weight of hydrogen storage alloy granules. The bulk specific weight of the mixture is 3.6 g·cm⁻³. The operation of the hydrogen storage container is as follows. At first, the pressure in the container is adjusted to 133 Pa. Then, hydrogen of 99.99% purity is filled into the container under a pressure of 4.0 MPa. The hydrogen storage alloy granules start to absorb hydrogen and are transformed into hydride. The hydrogen storage container is saturated when all the hydrogen storage alloy granules are transformed into hydride granules, a part of which crumbles into granules of smaller size. The hydrogen storage container is now activated and ready for use.

Test results show that, the weight density of hydrogen in the mixture is 1.4%. The thermal conductivity of the mixture is 5.2 J·m⁻¹·s⁻¹·k⁻¹. Neither deformation, nor damage of the container have been detected after the container is cycled 1000 times at the room temperature and a hydrogen charging pressure of 4.0 MPa.

EXAMPLE 2

The hydrogen storage alloy for the granules in the mixture is the titanium-based alloy TiFe_(0.85)Mn_(0.15). The non-hydrogen-absorbing alloy fibers are made of brass, with an average length of 11 mm and average cross section 1.2 mm². The weight ratio of brass fibers to hydrogen storage alloy granules is about 0.05. The bulk specific weight of the mixture is 3.0 g·cm⁻³. The process of activation and initial charging is similar to those of Example 1. The test results show that the hydrogen storage capacity is 1.7%. Neither damage nor deformation of the container have been detected after 1000 hydriding/dehydriding cycles.

EXAMPLE 3

Magnesium based alloy Mg₂Ni is used for the hydrogen storage alloy in the mixture of this example. The non-hydrogen-absorbing alloy for making alloy fibers is nickel alloy. The average length of the nickel alloy fibers is 20 mm, and their average cross sectional area is 2 mm². The weight ratio of the nickel alloy fibers to the hydrogen storage magnesium based alloy is about 0.1. The size of hydrogen storage alloy granules initially loaded into the containers should be under 5 mm in diameter. The bulk density of the mixture is 2.2 g·cm⁻³. In this example, pre-heating of the container is necessary for hydrogen absorbing and desorbing. The container is heated to 300° C. and the pressure is adjusted to 50 Pa before the initial charging of hydrogen. Then, the container is charged with hydrogen of 99.99% purity at a pressure of 3.0 MPa. Then, the activation and hydriding of Mg₂Ni can be started. During hydriding, Mg₂Ni transforms to Mg₂NiH₄. The test results show that the hydrogen storage capacity is 3.25%, no damage or deformation of the container has been detected after 1000 hydriding/dehydriding cycles. 

1. A hydrogen storage container comprising a container casing, a hydrogen storage mixture loaded into the container and a valve installed at an opening of the container, wherein, said mixture is made of granules of hydrogen storage materials and fibers of metals and/or metal alloys that do not absorb hydrogen said fibers being dispersed among the granules and form a network structure, and said fibers including metal fibers and/or alloy fibers, or their mixture.
 2. The hydrogen storage container according to claim 1, the metallic fibers in the mixture are made of aluminum, or copper, or nickel, or a mixture of the fibers of one or more metal selected from the group of aluminum, copper, and nickel.
 3. The hydrogen storage container according to claim 1, the alloy fibers in the mixture are made of aluminum alloy, or copper alloy, or nickel alloy, or a mixture of the fibers of one or more alloy selected from the group of aluminum alloy, copper alloy, and nickel alloy.
 4. The hydrogen storage container according to claim 1, the metal and/or alloy fibers in the mixture are a mixture of the fibers of aluminum/aluminum alloy, copper/copper alloy, and nickel/nickel alloy.
 5. The hydrogen storage container according to claim 1, the metallic fibers in the mixture have cut sections with filar shape.
 6. The hydrogen storage container according to claim 1, the metallic fibers in the mixture have cut sections with strip shape.
 7. The hydrogen storage container according to claim 1, wherein the dimension of the metal and/or alloy fibers are about 3˜20 mm in length and not more than 2 square millimeter in cross section.
 8. A hydrogen storage mixture for absorbing and desorbing hydrogen reversibly, said mixture being adapted to be placed in a hydrogen storage container and comprising granules of a hydrogen storage material and fibers of metals or metal alloys that do not absorb hydrogen, wherein the weight ratio of the fibers to the granules is about 0.01˜0.1. 